The British X Craft WWII Submarine

[Rpmtech1]

Clever idea, Thanks. I'll check it out when I start on this thing and get to that point.

[Slats]

The most important thing here before anyone departs from scale is working out if the model we are talking about was simply built too heavy.
Also how was the boat's GOG established? If its not dialed in right with little regard to CP / COR then its folly to chase down a possible not required un scale solution.

[Rpmtech1]

I dont think it will be an issue. Of course it has to be tested and we'll work it out.

[Subculture]

Many of these questions would be better answered by the builder. You can speak with him over on the AMS forum if you wish.

I can give some answers though. The C.G was alterable on this boat. It had two battery packs either side (lengthwise) of a central ballast tank which could be moved by servos. This means you can control the boat at low speed without touching the hydroplanes, and also trim the boat statically to perfection just by moving a slider.

The boat used a bag with a geared water pump for the ballast system, which gives very accurate trim. It's a wet hull boat and uses a WTC, which I think was 110mm or 120mm in diameter.

[Slats]

The size of the diameter of the WTC described by Andy "110- 120mm", (more than 4"), speaks volumes for me, a smaller diameter of 3" or less would provide I believe a noticeable handling improvement. Why? Because at this scale 1:12 (?), a 4" plus WTC diameter represents almost the entire beam of the sub save for 17mm either side of the WTC (with 110mm diameter WTC) 12.5mm either side (with 120mm diameter WTC). We are almost heading into equivalent dry hulled real estate and all the mass that occupies, particularly weight down low to offset the buoyancy inside the WTC. Happy to be wrong on that hypothesis.

I have mucked around with different setups and cylinders for the last decade. I have improved in a lot of cases the turning circle of boats by 30% or more simply by dropping the size of the cylinder by albeit a half inch, and a minimal drop in weight, usually commensurate completely with the lessened weight of cylinder material and not the internal equipment. Often with the upper buoyancy reduction of the reduced cylinder you can then shed some stabilising weight down below too. - Much of what I have learned comes from David's Cabal reports.

A case of suck it and see - but the science of the hobby built into to the suck means you will more often than not see pleasing results. - If you nail the COR / CP and COG once and for all its a big advantage.

Sorry but I can't see why with a single screw and control surfaces aft you would not have great control. - So therefore to me its got to be a question of too much mass momentum of the hull proper and the boats setup? If not what other physics is at play?


J

[Subculture]

Perhaps weight distribution is more of an important factor than overall displacement?

After all, if a heavy boat resulted in indifferent handling, why does a boat like an Engel Lafayette (dry hull) handle so well.

[Slats]

Perhaps weight distribution is more of an important factor than overall displacement?

After all, if a heavy boat resulted in indifferent handling, why does a boat like an Engel Lafayette (dry hull) handle so well.

Yeah Andy - perhaps it is. But I do find this model puzzling? Love to know more about the science at play here.
J

[Subculture]

I would think this boils down to inertial forces e.g. Newtons First Law.

A heavy boat is going to take more persuasion to alter it's current course than a lighter one.

The theory gets very complex, and I'm not ashamed to admit it boggles my mind.

One disadvantage I've observed of light boats is that they are more likely to be effected by chop when on the surface, i.e. it will bob about a bit in an un-scale manner. Whereas a heavier boat will ride the tide better.

[Kazzer]

As I start to get the various components together for this kit, I thought I'd list them here. The aft section of my model was crushed during delivery so I have some rebuilding to do.


A. The support struts marked A are K&S 1/4" Aluminum Streamline stock # 1100 . 4 x 3.5" sections

B. The control arms for the rudder are made from K&S Brass Stock 1/4" x 1/16" x 1.5". This is embedded in the resin upper rudder. It has a 1/8" holes drilled to accept the rudder shaft. Push-rod connectors still to be worked out.

C. The Dive Plane Bearings are Dubro 3/32" Shaft Collars. (Cat # 138) Cut a length of 3/32" brass rod, slightly taper the end and thread it onto the rod. It will cut it's own thread. The solder or CA adhesive it to secure. Finally, drill a 3/32" hole into the end of the horizontal stabilizer parallel to the outer edge. Insert the rod and CA the into place.

The shaft is 3/32" brass rod, the ends of this shaft accept a brass nut. Inserted into the dive plane as it is molded is a 3/32 ID brass tube. The tube needs trimming off where it is exposed in the center groove, and on the outer ends. The tube acts as a bushing

D. The propeller. A Raboesch 2" diam #176-12 Type A

[Kazzer]

I'm making the other half of the molds here. Firstly, I'm mixing very dry and sharp sand into the epoxy resin to make a resin rich sloppy mortar. I've never had a bubble or defect doing this and I think these are the reasons why.

1. The sand acts to cut through the resin as its mixed and it helps the air pockets, bubbles work free.
2. The sand particles are each dimensionally stable. As they touch each other, they make the resin dimensionally stable too. Zero shrinkage on cure. Imagine a bucket full of marbles. Each marble resting against another in every direction. Then pour resin in, all the resin does is glue each marble together and fill the gaps - simple.

3.The sand makes the mold harder and more resistant to wear. It is also less likely to warp or distort.




Here you can see the sloppy mix I use. You could also use polyester resin. I doubt mortar made this way would shrink using a sand filler.




Here are the 2 molds, surfaces duly waxed up and ready to go.


The finished pour.
After pouring, I shake and rattle the mold on the work bench to help remove any bubbles. Notice them on the surface of the mold.

[Kazzer]

And now! The moment of truth as I prize apart the molds and remove the plugs!

Ta! DAAAA!





Here is the dive plane. I placed clay cones in the lower section before pouring the resin, to give me vents and pouring holes. Before I make the actual product, I have to cut a length of 3/32" rod and some 3/32" id brass tube. This will be slotted across the plane to encapsulate the tube. If you look at the upper mold, then lower left, you'll see a small slot. This will house the brass control arm with the brass tube running through it.




Here's the horizontal stabilizers - chicken legs - or dive plane thingies. Note that I marked the holes and partially pre-drilled them.

Yes! That was a good mornings work! I've earned a beer!

[Kazzer]

My first pour of resin into the new molds came off pretty well. I mixed up some phenol novolac epoxy and added some black dye, and then added a little chopped strand glass. It didn't work out quite like I thought it would as the resin gelled up a little and didn't pour well. However, all was well and the thicker material glugged its way into the mold and saved the day.





The spew needs to be cleaned off, but the casting is -- G O O D !

NEXT!


I set the brass-work into the mold, the control arm fits tightly into its slot, and the dummy shft is well greased up with release agent.



Note the bushings at either end of the shaft. They are not waxed, as they need to be bonded into the dive plane. The bushings are simply short pieces of brass tube.

[jlday1256]

Man you have got to be having fun...by the way, it's sprue, not spew....

[He Who Shall Not Be Named]

Mike,

Good looking tool (I would have gone the rubber route). It will be terribly exciting if the same sand/resin mix turns out to be a viable means of making large hard-shell tools for GRP lay-up work. I'm watching this thread with interest.

David,

[Kazzer]

Man you have got to be having fun...by the way, it's sprue, not spew....

Well, it looks like spew and is all over the place, but I thought sprue referred to hot metal? That's my excuse - and I'm stickin' to it! :-)

I don't use much rubber and usually throw more away because it's gone off through old age, so prefer this idea. Maybe one side could be rubber, which would make de-molding easier?

Tomorrow, I may pluck up the courage to pour the M1 mold. It's had 3 coats of wax and is now in an MDF box.. A coat or two of PVA in the morning - then the moment of truth.

If that goes well, I'll start thinking of molding the X Craft master hull Alan Poole gave me specifically so I could reproduce his hull. It's been hanging around too long and needs to get done.